Tensioning device for cable window lifter

ABSTRACT

The invention concerns a tensioning device for the cable of a cable window lifter which is mounted in a drive bracket pulled up and down along a guide rail by means of a cable wound around an actuation drum. One cable end is solidly joined to the drive bracket whereas the other cable end is connected by a directional lock to the drive bracket. This directional lock compensates any cable elongation taking place within the cable actuation system by means of spring action. The tensioning device of the invention is characterized by providing further compensating means. This further compensation is needed in the event of excessive stresses exerted on the cable actuation system in the closed window position which results in a spurious cable elongation caused thereby. It also eliminates this compensation when this excess stress is no longer present. These further compensation means may consist of a spring additionally inserted between the free cable end and the directional lock; however they may also consist of a tippable and displaceable molded part inside the directional lock. The spring compensates the spurious cable elongation by relaxing before the actual compensation spring becomes effective. In the embodiments with the additionally inserted molded part, the compensation of the spurious elongation takes place by tipping the molded part which slips further by one step (cog) in the directional lock and only upon a real cable elongation.

BACKGROUND OF THE INVENTION

The invention concerns a tensioning device for the cable of a windowlifter of a vehicle.

It is known to the state of the art to fasten the two cable ends of thewindow lifter to the drive bracket and thereby to pull this drive meansup and down a guide rail. However it is inevitable during the operationof the window lifter that the cable shall gradually stretch and therebythat play will arise in this cable connection, this play making itselffelt when the window lift is actuated, for instance by a crank as a deadzone. It is further known to mount a cable-tensioning device at thedrive bracket so that the cable stretching is compensated by a spring.Such a tensioning device is disclosed in West German Patent No. 37 37733 and U.S. Pat. No. 4,235,046 the disclosures of which areincorporated herein by reference.

However cable stretching appears in cable window lifters not only as anaging effect but it also may arise when the window moves into its upperend position, wherein the drive bracket comes to rest against a stop,excessive force is applied to the crank to artificially elongate the"upper" cable segment between the cable drum and the drive bracket orthe guide rail becomes so warped that cable slack arises between thecable drum and the drive bracket. Such cable slack disappears once thewindow is moved down. Therefore the tensioning device may not becomeoperative when such a spurious, mostly slight cable elongation takesplace.

However the known tensioning devices also compensate for such artificialcable elongations. As a result, the cable system for all its ensuingservice life is harder to operate, at least until a real cableelongation eliminates this tension.

SUMMARY OF THE INVENTION

Having in mind the limitations of the prior art it is an object of thepresent invention to create a tensioning device whereby the cable slackgenerated by excessive force applied to the crank is compensated forseparately so that during the next down motion of the window pane, thiscable slack is again normally absorbed by the system while thetensioning device proper only becomes operative after actual cablestretching has taken place.

This object is achieved in a first embodiment by inserting an additionalspring into the tensioning device, where this additional spring isstronger than the actual compensating spring and for the same forcecovers a longer path. This means that the spring characteristics of thetwo springs are appropriately matched to each other.

In a second embodiment a tipping molded part is inserted between thedrive bracket and one cable end and is provided with a cog by means ofwhich it merely points in one direction or another in a cogged rack ofthe drive bracket when there is slight cable slack caused by excessiveapplied force, whereas in the event of actual cable elongation, it jumpsinto the next cog gap of the cogged rack.

A third embodiment includes a solution in the form of a displaceable andtippable part guided in the drive bracket on a long pin designed as acogged rack. In this embodiment the tippable part is a small platesuspended by an aperture from the pin.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated in the drawings in the form ofthree embodiments, wherein:

FIG. 1 is an elevation of the tensioning device of the first embodimentshown in the rest position;

FIG. 2 is an elevation of the tensioning device of the first embodimentshown in the operational position;

FIG. 3 is an elevation of the tensioning device of the second embodimentshown in the rest position;

FIG. 4 is an elevation of the tensioning device of the second embodimentshown in the operational position;

FIG. 5 is an elevation of the tensioning device of the third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the drive bracket 1 in which a U-shaped sheetmetal bail 2is supported in a displaceable manner, with its U-leg ends bent to theoutside in the form of hooks 12. Parts 1 and 2 act as a directional lock4 which on one hands consists of a cogged rack 4a having sawtoothnotches 4 at the drive bracket 1 and on the other hand of the alreadymentioned hooks at part 2. The hooks elastically engage the notches andtogether form the directional lock.

A cable 3 acts on the drive bracket 1 and is fastened to it by one end,the other end being connected to the sheetmetal bail 2.

A compression spring 5 is inserted between the drive bracket 1 and thesheetmetal bail 2. As easily noted from inspection, this spring forcesthe sheetmetal bail 2 ever more upward when cable elongation takesplace, the cogs 4b in the cogged rack 4a ever being depressed by anothertooth. As a result a dead zone in the window lift system is avoided,every cable elongation being compensated by the stepping of thesheetmetal bail 2.

The components shown and described so far are a tensioning device of thestate of the art. In the present invention on the other hand, a furtherspring 7 is inserted between the cable end fitting 3a and the sheetmetalbail 2. The cable fitting 3a can be raised by this spring 7 in thehook-shaped sheetmetal bail 2. Ordinarily the spring 7 is compressed sothat all its turns touch against each other i.e., it is compressed intoa solid block (FIG. 1). If now the drive bracket 1 is moved into itsupper end position (FIG. 1) and there rests for instance against a stop8, then the user, by excessively driving the schematically shown crank 9and the cable drum 10 tensions the cable in its upper half while thelower cable loop part slackens, for instance by warping the (omitted)guide rail. This is indicated in FIG. 1 by the waviness 14 of the cableloop part, the remaining guide elements for the cable such as guidetubes, rollers and the like having been omitted from the drawing for thesake of simplicity.

If the spring 7 were absent, the spring 5 would be operative at once,and the hook-shaped sheetmetal bail 2 would be forced up by another cog.As a result, the entire actuation system would be tensioned more, andsuch increased tension would not drop after the cable drum is rotated inthe opposite direction--once the window is lowered again. Rather theentire window system is harder to operate.

That drawback is circumvented in the embodiment shown in FIG. 1 and FIG.2 by the spring 7 first relaxing and thereby the almost spurious cableelongation being removed from the cable 3. Therefore the cable remainstaut also in its lower loop half as shown in FIG. 2.

When the drive means 1 together with the (omitted) window pane islowered again, then the spring 7 first is forced, by means of the cableend fitting 3a, to again form a solid block and only thereafter is theentire drive bracket 1 moved downward.

The operation above is always assured provided that the spring 7 is sodimensioned that it shall only differ in length by a few millimeters,for instance 2-3 mm, between its fully compressed, block-like conditionand its fully relaxed state, that is precisely over the distance bywhich from experience a user may tension the upper cable loop orelongate the lower one. Moreover the spring 7 is stronger than thespring 5.

The spring 5 becomes operative only after the spring 7 has been fullyrelaxed and nevertheless cable elongation is present in the lower cableloop, and then the hook-shaped sheetmetal bail 2 in the directional lock4 is moved by another cog by said spring 5. Thereupon the same initialconditions apply once more.

The same compensation capability is offered by the second embodimentshown in FIGS. 3 and 4; however this embodiment does not require theadditional spring 7.

This goal is achieved in that the cable fitting 3a terminates in amolded part 11 capable, on account of its shape, of assuming an obliqueposition in the guide duct of the drive means 1.

This second embodiment again includes the drive bracket 1 comprising thecogged rack 4a. The cable 3 passes through a casing 16 receiving thespring 5 which on the other hand rests on the drive bracket 1. Howeverthe cable 3 also passes through the molded part 11 and thereuponterminates into its end fitting 3a. The directional lock 4 is operativebetween a cog 4b of the molded part 11 and the cogged rack 4a.

If now the lower part of the cable 3 should elongate, then it is firstcompensated by the relaxation of the spring 5. Thereby the molded part11 shall be forced into an oblique position (FIG. 4), without thedirectional lock responding. It is only after the cable elongationexceeds a given value that the spring 5 shall press the cog of themolded part 11 out of the cogged rack 4a into the next higher gapbetween these cogs 4b.

Accordingly this second embodiment operates in the same manner as thatof FIGS. 1 and 2. A slight elongation of cable 3--for instance onaccount of excessive force applied to the crank 9--is removed from thecable loop without the directional lock becoming operative. When thedrive means moves in the opposite direction, that compensation iseliminated again. The directional lock 4 compensates only a moresubstantial elongation of the cable, and this compensation is noteliminated when the drive means descends but instead remains as aconstant compensation in the overall system.

A third embodiment operating in the same manner but differing in designis shown in FIG. 5. In this embodiment, a special pin 18 is inserted inthe drive bracket 1 and comprises a cogging 18a. The pin 18 is seated ina cross-shaded insert 1a which in turn is inserted in a groove or thelike present in the drive bracket 1.

The pin 18 is enclosed by a small plate 15 displaceable by means of anaperture relative to the pin 18. The cable 3 passes through anotheraperture in the small plate 15 and terminates in an end fitting 3a. Thespring 5 touches the pin 18 and rests on one hand on the drive bracket1, i.e., the inset 1a, and on the other hand on the small plate 15 whichit forces into the oblique position shown in FIG. 5. In that position,one of the edges of the aperture of the small plate is behind a cog ofthe pin 18.

The operation of the embodiment corresponds to that of FIGS. 3 and 4.When a slight slack arises in the lower cable loop, then it iscompensated by the spring 5 slightly lifting the small plate 15, thatis, the small plate of the FIG. 5 is forced into an approximatelyhorizontal position. This slight compensation is removed again from theactuation system once the drive bracket of FIG. 5 is pulled down.Thereupon the small plate again assumes its oblique position.

Only after the cable elongation becomes so large that the small plate 15can slip ahead by one cog is permanent compensation of this elongationintroduced automatically.

I claim:
 1. A cable actuated window lifter, comprising:an actuating drummounted in the body of a vehicle, a window drive bracket mounted forvertical adjustment in said vehicle body, a cable actuated by said drumwith a first end solidly joined to said drive and having a second end, atensioning device defined by a directional lock mounted on said drivebracket and connected to said second end, and said directional lockcomprising: a cogged rack, a part displaceable relative to said rackhaving cog means for engaging said rack and articulated on said secondend, a compression spring surrounding said cable and located betweensaid bracket and said displaceable part for compensation of cableelongation, said first compression spring always stressing saiddisplaceable part with said second cable end articulating on it in thedirection of cable tautening relative to said drive bracket, and saiddisplaceable part comprising a small plate and said cogged rackcomprising a pin with cogs, said small plate by means of an apertureslipping on said pin and engaging by means of said aperture edge saidcogs of said cogged rack, and said second cable end linked inarticulating manner to said small plate and acting on said compressionspring which initially tips said small plate on said pin during cableelongation in the direction of cable tautening and, upon further cableelongation, forces said small plate out of a first cog and into a secondcog.